The pelvic-pouch procedure has become a standard operation for selected patients with ulcerative colitis, but is contraindicated in patients with Crohn's disease at our institution. However, the distinction between ulcerative colitis and Crohn's colitis can sometimes be difficult, if not impossible. Between January 1982, and March 1989, 272 patients with ulcerative colitis underwent pelvic-pouch procedures at our institution. Nine (3.5 percent) of these patients eventually were found to have Crohn's disease. The records of these patients were examined to assess their clinical outcome and complication rate. There were five females and four males with a mean age of 28.8 years. In five patients (Group I) the diagnosis of Crohn's disease was made postoperatively on histologic examination of the rectum. The ileostomy was closed in all patients. Two developed complications necessitating excision of the pouch. Three patients are well. In the other four cases (Group II) the mean time to diagnosis was 2.5 years after the pouch procedure. Three patients developed pouch-vaginal fistula, and one multiple anal fissures and stenosis. Two required excision of the pouch whereas two have a functioning pouch but with a persistent pouch-vaginal fistula (n = 1) or anal fissures (n = 1). Overall, four patients have had their pouches removed, and five patients have functioning pouches: three with no complications and two with persistent perianal disease. Thus, we would conclude that the pelvic-pouch procedure should not knowingly be performed in patients with Crohn's disease because of the high associated complication rate.